Battery drain or faulty battery

[b3oty]

I only bought my 2001 3.0d a couple of weeks ago and the battery has been dead twice in the morning (both times I was playing with the sat nav the night before with the engine off). But even if I just lock it up and leave it until the next day after using it, starting is a bit slow suggesting the battery voltage is quite low.

I've read a lot on forums about parasitic battery drain, but I don't know if this is the problem, or if it just needs a new battery as I have no idea when it was last replaced.

So I gave the battery a full charge yesterday and when I removed the charger last night, it was showing 12.82 volts on my multi-meter.

I'm told a fully charged battery should be 12.60 volts after 24 hours of rest. I couldn't leave it that long as I need to use the car, but after 12 hours of rest the battery was only showing 12.40 which I gather is only about 75% charged.

So I presume that either the battery is past it's usefull life and can no longer hold a charge and therefore needs replacing, or something is drawing power when the car is locked and left overnight.

Can anyone tell me how I can tell which is the case please?

[b3oty]

I forgot to mention, there are no problems with the lights, the car seems to go into sleep mode OK and there are no problems with the climate control fans.

[b3oty]

UPDATE:

I took the car to have the battery tested today.

The tester tested the alternator and that was fine.

He said the battery is in very good condition and the cranking amps are high, but the voltage was still only 12.4v.

He said something must be draining the battery, so he attached a gadget to the battery positive cable and we closed and locked the car and waited 16 minutes for it to go into full sleep mode. At this point he read the draw and it was only 40ma. So it appears there is no parasitic draw when the car is locked and asleep overnight.

So apparently the battery is good and there is nothing drawing from it when it's left locked!

He could not understand why the battery is only at 12.4v when it should be at least 12.5v (preferably 12.6v) when the battery is good and the draw is low when the car is "asleep".

I wondered if the battery fitted is not heavy duty enough as it's rated at 88ah and 750amps as their system recommended a battery with 100ah and 900amps. But this seems unlikely as I have read the OEM battery is only 90ah and 720amps.

Can anyone shed any light on this please?

[b3oty]

UPDATE:

I tested the battery again this morning and the voltage had fallen to 12.25v.

Is there no one on this forum who can offer any help with this?

[bastereo]

Well, I would try disconnecting the battery and leave it to sit overnight or two and test the batter then.
But there really are only 2 ways a battery dies when the car is off: there is a parasitic drain or its a bad battery.

[JCL]

Just replace the battery.

[b3oty]

Originally Posted by bastereo

Well, I would try disconnecting the battery and leave it to sit overnight or two and test the batter then.
But there really are only 2 ways a battery dies when the car is off: there is a parasitic drain or its a bad battery.

Thank you for the reply. I think it's actually a bad battery (despite the person who tested it thinking it was ok). I tried another test I read about somewhere. I charged it up yesterday and left it for 5 minutes before checking the voltage at 12.8v. I then switched the headlights on for 1 minute, then tested the voltage again (with headlights still on) and voltage had fallen to well under 12v. I then switched the lights off and gave the battery a couple of minutes to recover and it only showed 12.34v. So I'm pretty sure it's a bad battery.

[b3oty]

Originally Posted by JCL

Just replace the battery.

That is what I've decided to do now. But I didn't want to waste £100 unnecessarily

[bmwmmn]

Had same problem, battery was having cell issues, replaced it and everything was fine afterwards!

[b3oty]

Originally Posted by bmwmmn

Had same problem, battery was having cell issues, replaced it and everything was fine afterwards!

I fitted a nice new Bosch one today. All good so far